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Expectation of food excites brain's hunger centres

A new study has revealed that even the expectation of food sparks the brain's hunger centres. The research, which is partly funded by the EU, is published in the October edition of Cell Metabolism.
The scientists provided food for rats during the same two hour period every da...

A new study has revealed that even the expectation of food sparks the brain's hunger centres. The research, which is partly funded by the EU, is published in the October edition of Cell Metabolism.
The scientists provided food for rats during the same two hour period every day. Once the rats had become accustomed to this regime, the researchers analysed what was going on in their brains before and during the meal times. They did this by measuring the levels of a protein called Fos in the different areas of the mice's brains, as many neurons produce Fos when they are activated.
The researchers found that before feeding, most of the brain areas examined showed relatively low levels of activity. However, at the usual feeding time, some of the areas of the brain containing appetite stimulators were active, even in rats which were not fed.
In rats which were fed, more 'hunger centres' were activated when the first bites of food were taken. 'The drive to eat is massively stimulated by the start of eating,' said Gareth Leng of the University of Edinburgh and one of the authors of the study. 'This shows the appetising effect of food itself as hunger circuits are acutely switched on.'
The researchers were surprised to find that brain areas which are linked with appetite suppression were also activated early on during the meal. Prior to the experiments, they had expected these 'satiety circuits' to remain inactive until a certain amount of food had been eaten.
'We had expected there to be a clear temporal dissociation between brain regions activated by hunger, which would peak at the scheduled time of food presentation and regions activated when the rats stopped eating,' the researchers write. 'Instead, neurons that release orexigenic peptides [appetite stimulating factors] appear to be activated by the imminent expectation of food, and neurons implicated in satiety are activated as soon as any food is eaten.'
Further research is now needed to understand how these shifts in brain activity are influenced by hormones, including the fat-generated hormone leptin, which signals the body's longer-term energy status.
The study is part of the EU-funded Diabesity project, which aims to identify genes involved in obesity and type 2 diabetes and study how these interact with systems regulating appetite and metabolism. Ultimately, the partners hope this information will lead to the identification of drug targets for the prevention of obesity and diabetes.